U.S. patent application number 11/944287 was filed with the patent office on 2010-11-18 for anti-tarnish coatings.
This patent application is currently assigned to Enthone Inc.. Invention is credited to Joseph A. Abys, Theodore Antonellis, Shenliang Sun.
Application Number | 20100291303 11/944287 |
Document ID | / |
Family ID | 40667834 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100291303 |
Kind Code |
A1 |
Abys; Joseph A. ; et
al. |
November 18, 2010 |
ANTI-TARNISH COATINGS
Abstract
A method is disclosed for enhancing the corrosion resistance of
a surface of a copper or copper alloy substrate. The method
comprises depositing a metallic surface layer comprising a precious
metal on a surface of the copper or copper alloy substrate by
immersion displacement plating and exposing the electronic device
to an aqueous composition comprising a first organic molecule
comprising at least one functional group that interacts with and
protects precious metal surfaces and a second organic molecule
comprising at least one functional group that interacts with and
protects copper surfaces.
Inventors: |
Abys; Joseph A.; (Warren,
NJ) ; Sun; Shenliang; (Bethany, CT) ;
Antonellis; Theodore; (Bethany, CT) |
Correspondence
Address: |
SENNIGER POWERS LLP
100 NORTH BROADWAY, 17TH FLOOR
ST LOUIS
MO
63102
US
|
Assignee: |
Enthone Inc.
West Haven
CT
|
Family ID: |
40667834 |
Appl. No.: |
11/944287 |
Filed: |
November 21, 2007 |
Current U.S.
Class: |
427/343 |
Current CPC
Class: |
H05K 2203/124 20130101;
C23F 11/10 20130101; C23C 18/54 20130101; C23F 11/149 20130101;
H05K 2203/122 20130101; C09D 5/086 20130101; H05K 3/282 20130101;
C23F 11/161 20130101; C09D 7/45 20180101; C08K 5/37 20130101; H05K
3/244 20130101; C08K 5/17 20130101; C09D 7/63 20180101 |
Class at
Publication: |
427/343 |
International
Class: |
B05D 3/10 20060101
B05D003/10 |
Claims
1. A method for enhancing the corrosion resistance of a surface of
a copper or copper alloy substrate, the method comprising:
depositing a metallic surface layer comprising a precious metal on
the surface of the copper or copper alloy substrate; and exposing
the copper or copper alloy substrate having the metallic surface
layer thereon to an aqueous composition comprising (a) a first
organic molecule comprising at least one functional group that
interacts with and protects precious metal surfaces, (b) a second
organic molecule comprising at least one functional group that
interacts with and protects copper surfaces, and (c) a
surfactant.
2. The method of claim 1 wherein the metallic surface layer is
deposited by an immersion displacement plating process, and the
metallic surface layer comprises silver, gold, or a combination
thereof.
3. The method of claim 1 wherein the first organic molecule is
selected from the group consisting of thiols (mercaptans),
disulfides, thioethers, thioaldehydes, thioketones, and
combinations thereof.
4. The method of claim 3 wherein the first organic molecule is a
thiol having the following general structure (I): R.sub.1--S--H
Structure (I) wherein R.sub.1 is either a hydrocarbyl having
between one carbon atom and about 24 carbon atoms or an aryl having
between about five and about fourteen carbon atoms.
5. The method of claim 4 wherein the thiol is selected from the
group consisting of ethanethiol; 1-propanethiol; 2-propanethiol;
2-propene-1-thiol; 1-butanethiol; 2-butanethiol;
2-methyl-1-propanethiol; 2-methyl-2-propanethiol;
2-methyl-1-butanethiol; 1-pentanethiol;
2,2-dimethyl-1-propanethiol; 1-hexanethiol; 1,6-hexanedithiol;
1-heptanethiol; 2-ethylhexanethiol; 1-octanethiol;
1,8-octanedithiol; 1-nonanethiol; 1,9-nonanedithiol; 1-decanethiol;
1-adamantanethiol; 1,11-undecanedithiol; 1-undecanethiol;
1-dodecanethiol; tert-dodecylmercaptan; 1-tridecanethiol;
1-tetradecanethiol; 1-pentadecanethiol; 1-hexadecanethiol;
1-heptadecanethiol; 1-octadecanethiol; 1-nonadecanethiol; and
1-icosanethiol; and combinations thereof.
6. The method of claim 4 wherein the thiol is selected from the
group consisting of benzenethiol; 2-methylbenzenethiol;
3-methylbenzenethiol; 4-methylbenzenethiol; 2-ethylbenzenethiol;
3-ethylbenzenethiol; 4-ethylbenzenethiol; 2-propylbenzenethiol;
3-propylbenzenethiol; 4-propylbenzenethiol;
2-tert-butylbenzenethiol; 4-tert-butylbenzenethiol;
4-pentylbenzenethiol; 4-hexylbenzenethiol; 4-heptylbenzenethiol;
4-octylbenzenethiol; 4-nonylbenzenethiol; 4-decylbenzenethiol;
benzyl mercaptan; 2,4-xylenethiol, furfuryl mercaptan;
1-naphthalenethiol; 2-naphthalenethiol; 4,4'-dimercaptobiphenyl;
and combinations thereof.
7. The method of claim 3 wherein the first organic molecule is a
disulfide having the following structure (II):
R.sub.1--S--S--R.sub.2 Structure (II) wherein R.sub.1 and R.sub.2
are each independently either a hydrocarbyl having between one
carbon atom and about 24 carbon atoms or an aryl having between
about five and about fourteen carbon atoms.
8. The method of claim 7 wherein the disulfide is selected from the
group consisting of diethyl disulfide, di-n-propyl disulfide,
diisopropyl disulfide, diallyl disulfide, di-n-butyl disulfide,
di-sec-butyl disulfide, diisobutyl disulfide, di-tert-butyl
disulfide, di-n-pentyl disulfide, di-neopentyl disulfide,
di-n-hexyl disulfide, di-n-heptyl disulfide, di-n-octyl disulfide,
di-n-nonyl disulfide, di-n-decyl disulfide, di-n-dodecyl disulfide,
di-n-tridecyl disulfide, di-n-tetradecyl disulfide, di-n-pentadecyl
disulfide, di-n-hexadecyl disulfide, di-n-heptadecyl disulfide,
di-n-octadecyl disulfide, di-n-decyl disulfide; diundecyl
disulfide, didodecyl disulfide, dihexadecyl disulfide, dibenzyl
disulfide, dithienyl disulfide, 2-naphthyl disulfide, and
combinations thereof.
9. The method of claim 1 wherein the second organic molecule is
selected from the group consisting of primary amines, secondary
amines, tertiary amines, aromatic heterocycles comprising nitrogen,
and combinations thereof.
10. The method of claim 9 wherein the second organic molecule is a
primary amine, secondary amine, or a tertiary amine having the
following general structure (III): ##STR00024## wherein R.sub.1,
R.sub.2, and R.sub.3 are each independently hydrogen or a
hydrocarbyl having between one carbon atom and about 24 carbon
atoms, and at least one of R.sub.1, R.sub.2, and R.sub.3 is a
hydrocarbyl having between one carbon atom and about 24 carbon
atoms.
11. The method of claim 10 wherein the amine is selected from the
group consisting of aminoethane, 1-aminopropane, 2-aminopropane,
1-aminobutane, 2-aminobutane, 1-amino-2-methylpropane,
2-amino-2-methylpropane, 1-aminopentane, 2-aminopentane,
3-aminopentane, neo-pentylamine, 1-aminohexane, 1-aminoheptane,
2-aminoheptane, 1-aminooctane, 2-aminooctane, 1-aminononane,
1-aminodecane, 1-aminododecane, 1-aminotridecane,
1-aminotetradecane, 1-aminopentadecane, 1-aminohexadecane,
1-aminoheptadecane, 1-aminooctadecane, and combinations
thereof.
12. The method of claim 9 wherein the second organic molecule is an
azole having the following general structure (IV): ##STR00025##
wherein each of R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 is
an atom selected from the group consisting of carbon and nitrogen
wherein between one and four of the R.sub.1, R.sub.2, R.sub.3,
R.sub.4, and R.sub.5 groups are nitrogen and between one and four
of the R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 groups are
carbon; and R.sub.11, R.sub.22, R.sub.33, R.sub.44, and R.sub.55
are each independently selected from the group consisting of
hydrogen, carbon, sulfur, oxygen, and nitrogen.
13. The method of claim 12 wherein the azole is selected from the
group consisting of pyrrole (1H-azole); imidazole(1,3-diazole);
pyrazole(1,2-diazole); 1,2,3-triazole; 1,2,4-triazole; tetrazole;
isoindole; indole(1H-benzo[b]pyrrole);
benzimidazole(1,3-benzodiazole); indazole(1,2-benzodiazole);
1H-benzotriazole; 2H-benzotriazole; imidazo[4,5-b]pyridine;
purine(7H-imidazo(4,5-d)pyrimidine); pyrazolo[3,4-d]pyrimidine;
triazolo[4,5-d]pyrimidine; and combinations thereof.
14. The method of claim 12 wherein the azole is selected from the
group consisting of 2-(3,4-dichlorobenzyl)-benzimidazole;
2-bromobenzyl benzimidazole; 2-bromophenyl benzimidazole;
2-bromoethylphenyl benzimidazole; 2-chlorobenzyl benzimidazole;
2-chlorophenyl benzimidazole; 2-chloroethylphenyl benzimidazole;
and combinations thereof.
15. The method of claim 1 wherein the first organic molecule is
present in a concentration between about 1 and about 10 g/L and the
second organic molecule in a concentration between about 1 and
about 10 g/L.
16. A method for enhancing the corrosion resistance of a surface of
a copper or copper alloy substrate, the method comprising:
depositing a metallic surface layer comprising silver and/or gold
on the surface of the copper or copper alloy substrate; and
exposing the copper or copper alloy substrate having the metallic
surface layer thereon to an aqueous composition comprising (a) a
first organic molecule in a concentration between about 1 and about
10 g/L selected from the group consisting of thiols (mercaptans),
disulfides, thioethers, thioaldehydes, thioketones, and
combinations thereof that interacts with and protects precious
metal surfaces, (b) a second organic molecule in a concentration
between about 1 and about 10 g/L selected from the group consisting
of primary amines, secondary amines, tertiary amines, aromatic
heterocycles comprising nitrogen, and combinations thereof that
interacts with and protects copper surfaces, and (c) a
surfactant.
17. A method for enhancing the corrosion resistance of a surface of
a copper or copper alloy substrate, the method comprising:
depositing a metallic surface layer comprising silver and/or gold
on the surface of the copper or copper alloy substrate; and
exposing the copper or copper alloy substrate having the metallic
surface layer thereon to an aqueous composition comprising (a) a
first organic molecule of 1-octadecanethiol in a concentration
between about 1 and about 10 g/L, (b) a second organic molecule in
a concentration between about 1 and about 10 g/L selected from the
group consisting of primary amines, secondary amines, tertiary
amines, aromatic heterocycles comprising nitrogen, and combinations
thereof that interacts with and protects copper surfaces, and (c) a
surfactant.
Description
FIELD OF THE INVENTION
[0001] This invention relates to methods and compositions for
enhancing the corrosion protection, solderability, and wear
resistance of copper substrates used in the manufacture of
electronic and microelectronic devices.
BACKGROUND OF THE INVENTION
[0002] Metallic surface coatings are commonly applied to electronic
devices and decorative objects to provide corrosion protection and
other desired functional properties. Electronic devices comprising
copper or copper alloy substrates are typically coated with
metallic surface coatings which provide corrosion protection, high
surface contact conductivity, and wear resistance. The metallic
surface coatings typically comprise precious metals, in particular
silver and gold, which provide superior corrosion protection.
[0003] For example, in printed circuit board manufacture, a thin
layer of silver may be deposited over copper circuitry as a
solderability preserver. The silver is generally deposited by an
immersion displacement plating, in which silver ions present in the
plating composition come into contact with and are reduced by
surface copper atoms, according to the following reaction:
Cu.sub.(s)+2Ag.sup.+.sub.(aq)=>Cu.sup.2+.sub.(aq)+2Ag.sub.(s).
The reduction-oxidation reaction reduces silver ions to silver
metal and forms an adhesive silver layer over the copper substrate.
The process is self-limiting in that once the copper surface is
covered with a layer of silver, copper atoms are no longer
accessible to reduce additional silver ions. Typical thicknesses of
silver immersion displacement films over copper can be between
about 0.05 and about 0.8 microns. See, for example, U.S. Pat. Nos.
5,955,141; 6,319,543; 6,395,329; and 6,860,925, the disclosures of
which are hereby incorporated by reference as if set forth in their
entireties.
[0004] In the manufacture of copper lead frames and connectors and
as an alternative finish in PCB manufacture, gold may be applied as
a metallic surface coating over copper substrates for corrosion
resistance and increased wear resistance. Typically, gold is not
deposited directly on the copper substrate, but rather on an
intervening base metal underlayer. The base metal underlayer,
typically electrolessly deposited nickel, is deposited on the
copper or copper alloy substrate. The base metal serves as a
diffusion barrier. The precious metal overlayer, such as gold,
palladium, or alloys thereof, is then deposited, typically by an
immersion displacement method, over the base metal underlayer
coating. The precious metal overlayer provides corrosion
resistance, wear resistance, and high conductivity. In the
conventional electroless nickel-immersion gold method (commonly
referred to as ENIG), an electrolessly deposited nickel underlayer
increases the hardness of an immersion plated gold overlayer. This
metallic surface is commonly referred to as "nickel-hardened gold"
or simply, "hard gold." Variations on these coatings involve base
metal alloy underlayers, precious metal alloy overlayers, and
metallic surface coatings comprising two or more base metal
underlayers and/or two or more precious metal overlayers.
[0005] An obvious disadvantage to the use of precious metals such
as gold and palladium is cost. A cost effective connector uses a
precious metal coating layer which is as thin as possible, without
sacrificing the desired functional properties. Accordingly, the
industry typically employs precious metal layer on the order of
about 1.0 .mu.m thick on electronic connectors. Thinner layers
suffer from the disadvantage of highly increased porosity in the
coating. Over time in service, the thin layers having a high degree
of porosity are ineffective against base metal and copper diffusion
to the surface. In a corrosive environment, the exposed base metal
and copper will corrode and the corrosion product(s) can migrate
onto the coating surface and deteriorate the surface contact
conductivity. Moreover, a thin precious metal layer can wear off
during application and shorten the connector's useful lifetime.
[0006] A particular problem observed with immersion-plated precious
metal coatings, e.g., silver and gold, is creep corrosion of copper
salts at certain bare copper interfaces between copper and precious
metal. For example, immersion silver displacement plating processes
may not sufficiently coat copper wiring in PCB, particularly at
plated through holes and high aspect ratio blind vias. Corrosion at
these locations manifests itself as an annular ring surrounding the
vias and plated through holes.
[0007] Moreover, silver is susceptible to sulfidation by reduced
sulfur compounds (e.g., hydrogen sulfide) present in the
environment, particularly at paper processing plants, rubber
processing plants, and high pollution environments. Sufficient
sulfidation of silver can result in localized pores, which may
expose copper to the environment. Humidity and environmental
pollutants can oxidize and sulfidize the copper, forming copper
salts that may creep through pores in the silver layer.
SUMMARY OF THE INVENTION
[0008] In one aspect, the present invention is directed to a method
for enhancing the corrosion resistance of a surface of a copper or
copper alloy substrate. The method comprises depositing a metallic
surface layer comprising a precious metal on the surface of the
copper or copper alloy substrate; and exposing the copper or copper
alloy substrate having a metallic surface layer thereon to an
aqueous composition comprising (a) a first organic molecule
comprising at least one functional group that interacts with and
protects precious metal surfaces, (b) a second organic molecule
comprising at least one functional group that interacts with and
protects copper surfaces, and (c) a surfactant.
[0009] Other objects and features will be in part apparent and in
part pointed out hereinafter.
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1 is an illustration depicting two molecules adhering
to and forming a protective organic film on the surfaces of a
copper substrate having an immersion-plated silver layer
thereon.
[0011] FIGS. 2A through 2D are photographs of an immersion
silver-plated copper coupon coated with immersion-plated silver
according to the method of Example 1. The silver-plated copper
coupon was subjected to porosity testing according to the method of
Example 2.
[0012] FIGS. 3A and 3B are photographs of immersion silver-plated
copper coupons subjected to porosity testing according to the
method of Example 4.
[0013] FIGS. 4A through 4F are photographs of immersion
silver-plated copper coupons subjected to porosity testing
according to the method of Example 8.
[0014] FIGS. 5A through 5E are photographs of immersion
silver-plated copper coupons subjected to porosity testing
according to the method of Example 9.
DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION
[0015] The present invention is directed to a method and
composition for applying a protective organic film to a copper
substrate having a metallic coating on a surface thereof. In one
embodiment, the metallic coating comprises a precious metal. In one
embodiment, the method and composition apply a protective organic
film to a metallic coating comprising silver. In one embodiment
thereof, the metallic coating comprising silver is applied by an
immersion displacement plating process. In another embodiment, the
method and composition apply a protective organic film to a
metallic coating comprising gold. In one embodiment thereof, the
metallic coating comprising gold is applied by an immersion
displacement plating process.
[0016] The protective organic film is particularly suited for use
in preserving the solderability of copper or copper alloy
substrates having a layer of precious metal thereon. Copper
substrates suitable for protection with the organic protective film
of the invention include copper circuitry in printed circuit
boards, chip carriers, semiconductor substrates, metal lead frames,
and other solderable copper substrates. These substrates may be
coated with precious metal, in particular with metallic coatings
comprising silver, gold, or a combination thereof.
[0017] Silver immersion displacement plating is a particularly
preferred method of preserving the solderability of copper
conductive features and copper plated through holes in printed
circuit board (PCB) manufacture. Silver immersion plating is a
self-limiting process which yields silver layers having typical
thicknesses between about 0.05 microns and about 0.8 microns,
typically between about 0.15 microns and about 0.40 microns.
Certain immersion processes and compositions can plate silver
layers having thicknesses outside the broad range. As stated above,
immersion-plated silver may not adequately protect copper surfaces,
such as at certain bare copper interfaces between copper and
silver, particularly at plated through holes and high aspect ratio
blind vias in PCB substrates. Moreover, immersion-plated silver
coatings are susceptible to pore formation due to sulfidation and
oxidation, particularly in high pollution environments.
Accordingly, the present invention is directed to a method of
applying a protective organic film to provide a layer of corrosion
protection over copper surfaces, in addition to the
immersion-plated silver coating. In one embodiment, therefore, the
method of applying the protective organic film involves exposing
the copper substrate having an immersion-plated silver coating on a
surface thereof to a composition for enhancing the corrosion
resistance of the immersion-plated silver coating and for
maintaining the solderability of the copper conductive lines and
copper plated through holes.
[0018] The present invention is therefore further directed to such
a composition. The composition of the present invention comprises
an organic molecule comprising at least one functional group that
interacts with and protects precious metal surfaces. In particular,
the organic molecule comprises at least one functional group that
interacts with and protects silver surfaces, gold surfaces, or a
surface comprising both silver and gold. Such an organic molecule
is effective for filling pores in the precious metal layer, thereby
inhibiting copper creep corrosion, and is effective for covering
the surface of the precious metal with a self-assembled protective
organic film.
[0019] The present invention is further directed to a composition
that comprises an organic molecule comprising at least one organic
functional group that interacts with and protects copper surfaces.
Such an organic molecule is capable of reacting with copper
surfaces, thereby forming a self-assembled protective organic film
capable of inhibiting exposure to water, environmental humidity,
and other pollutants that may corrode copper surfaces.
[0020] The present invention is yet further directed to a
composition that comprises an organic molecule comprising at least
one functional group that interacts with and protects precious
metal surfaces and an organic molecule comprising at least one
organic functional group that interacts with and protects copper
surfaces.
[0021] In one embodiment, the organic molecule comprising at least
one functional group that interacts with and protects precious
metal surfaces comprises a sulfur atom. Functional groups that
comprise a sulfur atom include thiols (mercaptans), disulfides,
thioethers, thioaldehydes, and thioketones. The composition may
comprise a combination of thiols (mercaptans), disulfides,
thioethers, thioaldehydes, and thioketones. Without being bound to
a particular theory, it is thought that the lone electron pair in
the sulfur atom forms a sulfur-precious metal bond, thereby
self-assembling a protective organic film over the precious metal
coating layer, wherein the film comprises a self-assembled
monolayer comprising an organic molecule comprising the sulfur atom
bonded to the precious metal surface. In one embodiment, the copper
substrate is coated with a silver coating layer deposited by, for
example, immersion displacement plating, and the sulfur atom
present in the organic molecule forms a sulfur-silver bond. In one
embodiment, the copper substrate is coated with a gold coating
layer deposited by, for example, immersion displacement plating,
and the sulfur atom present in the organic molecule forms a
sulfur-gold bond. The sulfur containing compound typically
comprises an organic component that enhances the effectiveness of
the organic protective film by rendering the film more hydrophobic
and thus more capable of repelling water and environmental
humidity.
[0022] In one embodiment, the organic molecule comprising at least
one functional group that interacts with and protects precious
metal surfaces is a thiol. Thiols have the following general
structure (I):
R.sub.1--S--H Structure (I)
wherein R.sub.1 is a hydrocarbyl having from one carbon atom to
about 24 carbon atoms, an aryl having from about five to about
fourteen carbon atoms, or an arylhydrocarbyl wherein the
hydrocarbyl has from one carbon atom to about 24 carbon atoms and
the aryl has from about five to about fourteen carbon atoms. The
hydrocarbyl preferably comprises between about six carbon atoms and
about 18 carbon atoms. The aryl preferably comprises between about
four and about ten carbon atoms. The aryl may comprise one
five-membered ring or six-membered ring or a fused two-ring system
in which the two-rings include a five-membered ring and a
six-membered ring or two six-membered rings. The aryl and
hydrocarbyl may be substituted or unsubstituted. Typical
substituents include short carbon chain branching alkyl groups,
typically having from one to four carbon atoms, i.e., methyl,
ethyl, propyl, and butyl substituents and aromatic groups such as
phenyl, naphthenyl, and aromatic heterocycles comprising nitrogen,
oxygen, and sulfur. Other substituents include amines, thiols,
carboxylates, phosphates, phosphonates, sulfates, sulfonates,
halogen, hydroxyl, alkoxy, aryloxy, protected hydroxy, keto, acyl,
acyloxy, nitro, cyano, esters, and ethers. In one preferred
embodiment, the R.sub.1 is hydrocarbyl, is not substituted with
other groups, and is a straight-chained alkyl, since
straight-chained alkyl better achieves a desirable densely packed
self-assembled monolayer over the precious metal surface coating.
Exemplary alkyl thiols applicable for use in the composition of the
present invention include, singly or in combination, ethanethiol;
1-propanethiol; 2-propanethiol; 2-propene-1-thiol; 1-butanethiol;
2-butanethiol; 2-methyl-1-propanethiol; 2-methyl-2-propanethiol;
2-methyl-1-butanethiol; 1-pentanethiol;
2,2-dimethyl-1-propanethiol; 1-hexanethiol; 1,6-hexanedithiol;
1-heptanethiol; 2-ethylhexanethiol; 1-octanethiol;
1,8-octanedithiol; 1-nonanethiol; 1,9-nonanedithiol; 1-decanethiol;
1-adamantanethiol; 1,11-undecanedithiol; 1-undecanethiol;
1-dodecanethiol; tert-dodecylmercaptan; 1-tridecanethiol;
1-tetradecanethiol; 1-pentadecanethiol; 1-hexadecanethiol;
1-heptadecanethiol; 1-octadecanethiol; 1-nonadecanethiol; and
1-icosanethiol.
[0023] In another preferred embodiment, the R.sub.1 comprises an
aromatic ring. Aryl thiols also achieve highly hydrophobic, densely
packed self-assembled monolayers over the precious metal surface
coating. Exemplary aryl thiols applicable for use in the
composition of the present invention include, singly or in
combination, benzenethiol; 2-methylbenzenethiol;
3-methylbenzenethiol; 4-methylbenzenethiol; 2-ethylbenzenethiol;
3-ethylbenzenethiol; 4-ethylbenzenethiol; 2-propylbenzenethiol;
3-propylbenzenethiol; 4-propylbenzenethiol;
2-tert-butylbenzenethiol; 4-tert-butylbenzenethiol;
4-pentylbenzenethiol; 4-hexylbenzenethiol; 4-heptylbenzenethiol;
4-octylbenzenethiol; 4-nonylbenzenethiol; 4-decylbenzenethiol;
benzyl mercaptan; 2,4-xylenethiol, furfuryl mercaptan;
1-naphthalenethiol; 2-naphthalenethiol; and
4,4'-dimercaptobiphenyl.
[0024] In one embodiment, the organic molecule comprising at least
one functional group that interacts with and protects precious
metal surfaces is a disulfide. Disulfides can be formed by the
oxidation of two thiols and can have the following structure
(II):
R.sub.1--S--S--R.sub.2 Structure (II)
wherein R.sub.1 and R.sub.2 are each independently a hydrocarbyl
having between one carbon atom and about 24 carbon atoms, an aryl
having between about five and about fourteen carbon atoms, or an
arylhydrocarbyl wherein the hydrocarbyl has from one carbon atom to
about 24 carbon atoms and the aryl has from about five to about
fourteen carbon atoms. The hydrocarbyl preferably comprises between
about six carbon atoms and about 18 carbon atoms. The aryl
preferably comprises between about four and about ten carbon atoms.
The aryl may comprise one five-membered ring or six-membered ring
or a fused two-ring system in which the two-rings include a
five-membered ring and a six-membered ring or two six-membered
rings. The aryl and hydrocarbyl may be substituted or
unsubstituted. The aryl and hydrocarbyl may be substituted or
unsubstituted. Typical substituents include short carbon chain
branching alkyl groups, typically having from one to four carbon
atoms, i.e., methyl, ethyl, propyl, and butyl substituents and
aromatic groups such as phenyl, naphthenyl, and aromatic
heterocycles comprising nitrogen, oxygen, and sulfur. Other
substituents include amines, thiols, carboxylates, phosphates,
phosphonates, sulfates, sulfonates, halogen, hydroxyl, alkoxy,
aryloxy, protected hydroxy, keto, acyl, acyloxy, nitro, cyano,
esters, and ethers. In one preferred embodiment, the R.sub.1 and
R.sub.2 hydrocarbyls are not substituted with other groups and are
straight-chained alkyls, since straight-chained alkyls better
achieve a desirable densely packed self-assembled monolayer over
the precious metal surface coating. Exemplary disulfides applicable
for use in the composition of the present invention include, singly
or in combination, diethyl disulfide, di-n-propyl disulfide,
diisopropyl disulfide, diallyl disulfide, di-n-butyl disulfide,
di-sec-butyl disulfide, diisobutyl disulfide, di-tert-butyl
disulfide, di-n-pentyl disulfide, di-neopentyl disulfide,
di-n-hexyl disulfide, di-n-heptyl disulfide, di-n-octyl disulfide,
di-n-nonyl disulfide, di-n-decyl disulfide, di-n-dodecyl disulfide,
di-n-tridecyl disulfide, di-n-tetradecyl disulfide, di-n-pentadecyl
disulfide, di-n-hexadecyl disulfide, di-n-heptadecyl disulfide,
di-n-octadecyl disulfide, di-n-decyl disulfide; diundecyl
disulfide, didodecyl disulfide, dihexadecyl disulfide.
[0025] In another preferred embodiment, R.sub.1 and R.sub.2
comprises an aromatic ring. It is thought that the sulfur-sulfur
bond may be broken more easily for aromatic disulfides, such that
the sulfur atom is more easily made available for bonding to silver
or gold. Aryl thiols also achieve highly hydrophobic, densely
packed self-assembled monolayers over the precious metal surface
coating. Exemplary aryl thiols applicable for use in the
composition of the present invention include, singly or in
combination, dibenzyl disulfide, dithienyl disulfide, and
2-naphthyl disulfide.
[0026] The organic molecule comprising at least one functional
group that interacts with and protects precious metal surfaces may
be added to the surface treating compositions of the present
invention at a concentration between about 0.01% by weight (about
0.1 g/L) and about 10% by weight (about 100 g/L), preferably
between about 0.1% by weight (about 1.0 g/L) and about 1.0% by
weight (about 10 g/L). The sulfur containing compound is added to
the composition in at least 0.1 g/L to achieve adequate coverage
and protection of the surface coating. The maximum concentration of
about 100 g/L is an estimate based on the compound's solubility and
therefore may be higher or lower than the stated amount depending
upon the identity of the sulfur containing compound. In a preferred
composition, the organic molecule comprising at least one
functional group that interacts with and protects precious metal
surfaces is 1-octadecanethiol added in a concentration between
about 0.5 g/L and about 10.0 g/L, for example, about 5.0 g/L.
[0027] In one embodiment, the organic molecule comprising at least
one functional group that interacts with and protects copper
surfaces comprises a nitrogen atom. Accordingly, the organic
functional group is an amine. An amine is a functional group
comprising nitrogen, typically bonded to or part of an organic
functional group, such as a hydrocarbyl, an aryl, or an aromatic
heterocycle. Applicable amines therefore include primary amines,
secondary amines, tertiary amines, and aromatic heterocycles
comprising nitrogen. The composition may comprise a combination of
amines. Without being bound to a particular theory, it is thought
that the lone electron pair in the amine functional group forms a
nitrogen-copper bond, thereby forming a protective organic film
over the copper conducting layer, wherein the film comprises the
nitrogen atom of the amine bonded to the copper surface and the
organic substituent.
[0028] In one embodiment, the amine is a primary amine, secondary
amine, or a tertiary amine having the following general structure
(III):
##STR00001##
wherein R.sub.1, R.sub.2, and R.sub.3 are each independently
hydrogen or a hydrocarbyl having between one carbon atom and about
24 carbon atoms, and at least one of R.sub.1, R.sub.2, and R.sub.3
is a hydrocarbyl having between one carbon atom and about 24 carbon
atoms. The hydrocarbyl preferably comprises between about six
carbon atoms and about 18 carbon atoms. The hydrocarbyl may be
substituted or unsubstituted. Typical substituents include short
carbon chain branching alkyl groups, typically having from one to
four carbon atoms, i.e., methyl, ethyl, propyl, and butyl
substituents and aromatic groups such as phenyl, napthenyl, and
aromatic heterocycles comprising nitrogen, oxygen, and sulfur.
Other substituents include amines, thiols, carboxylates,
phosphates, phosphonates, sulfates, sulfonates, halogen, hydroxyl,
alkoxy, aryloxy, protected hydroxy, keto, acyl, acyloxy, nitro,
cyano, esters, and ethers. In one preferred embodiment, only one of
R.sub.1, R.sub.2, and R.sub.3 is an unsubstituted hydrocarbyl and a
straight chained alkyl, since a primary amine comprising a
straight-chained alkyl better achieves a desirable densely packed
self-assembled monolayer over a copper surface. Exemplary primary
amines applicable for use in the composition of the present
invention, singly or in combination, include aminoethane,
1-aminopropane, 2-aminopropane, 1-aminobutane, 2-aminobutane,
1-amino-2-methylpropane, 2-amino-2-methylpropane, 1-aminopentane,
2-aminopentane, 3-aminopentane, neo-pentylamine, 1-aminohexane,
1-aminoheptane, 2-aminoheptane, 1-aminooctane, 2-aminooctane,
1-aminononane, 1-aminodecane, 1-aminododecane, 1-aminotridecane,
1-aminotetradecane, 1-aminopentadecane, 1-aminohexadecane,
1-aminoheptadecane, and 1-aminooctadecane.
[0029] In a preferred embodiment, the organic functional group that
interacts with and protects copper surfaces is an aromatic
heterocycle comprising nitrogen. It is thought that aromatic
heterocycles comprising nitrogen additionally protect copper
surfaces by interacting with copper(I) ions on the surface of the
copper conducting layer. Interaction with copper(I) ions forms a
film comprising insoluble copper(I)-based organometallics that
precipitate on the surface of the copper conducting layer. This
precipitate is also thought to be another mechanism whereby amines,
particularly heterocyclic, aromatic amines, form a protective
organic film on the surface of the copper conducting layer.
[0030] Aromatic heterocycles comprising nitrogen suitable for the
use in the composition of the present invention comprise nitrogen
in a 5-membered ring (azoles). The 5-membered can be fused to
another 5-membered or 6-membered aromatic ring, which can also be a
heterocyclic ring comprising a nitrogen atom. Further, the aromatic
heterocycle can comprise one or more nitrogen atoms, and typically,
the aromatic heterocycle comprises between one and four nitrogen
atoms. Azoles can have the following general structure (IV):
##STR00002##
wherein each of R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 is
an atom selected from the group consisting of carbon and nitrogen
wherein between one and four of the R.sub.1, R.sub.2, R.sub.3,
R.sub.4, and R.sub.5 groups are nitrogen and between one and four
of the R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 groups are
carbon; and R.sub.11, R.sub.22, R.sub.33, R.sub.44, and R.sub.55
are each independently selected from the group consisting of
hydrogen, carbon, sulfur, oxygen, and nitrogen.
[0031] Any one or more of R.sub.11, R.sub.22, R.sub.33, R.sub.44,
and R.sub.55 of structure (I) may be carbon wherein the carbon is
part of an aliphatic group having between one carbon atom and 24
carbon atoms or part of an aryl group having between two carbon
atoms and fourteen carbon atoms. The aliphatic group and the aryl
group may be substituted or unsubstituted. The aliphatic group may
be branched-chained or straight-chained. Unless otherwise
indicated, a substituted aliphatic group or substituted aryl group
is substituted with at least one atom other than carbon, including
moieties in which a carbon chain atom is substituted with a hetero
atom such as nitrogen, oxygen, silicon, phosphorous, boron, sulfur,
or a halogen atom. The aliphatic group or aryl may be substituted
with one or more of the following substituents: halogen,
heterocyclo, alkoxy, alkenoxy, alkynoxy, aryloxy, hydroxy,
protected hydroxy, hydroxycarbonyl, keto, acyl, acyloxy, nitro,
amino, amido, nitro, phosphono, cyano, thiol, ketals, acetals,
esters, and ethers.
[0032] In structure (IV), any pair of consecutive R.sub.11,
R.sub.22, R.sub.33, R.sub.44, and R.sub.55 (e.g., R.sub.11 and
R.sub.22 or R.sub.22 and R.sub.33) can together with the carbon or
nitrogen atoms to which they are bonded form a substituted or
unsubstituted cycloalkyl or substituted or unsubstituted aryl group
with the corresponding pair of consecutive R.sub.1, R.sub.2,
R.sub.3, R.sub.4, and R.sub.5 (e.g., R.sub.11 and R.sub.22 form a
ring with R.sub.1 and R.sub.2) such that the ring defined by the
R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 groups is fused to
another ring. This ring may comprise one or two nitrogen atoms.
Preferably, the consecutive R.sub.11, R.sub.22, R.sub.33, R.sub.44,
and R.sub.55 and the corresponding consecutive R.sub.1, R.sub.2,
R.sub.3, R.sub.4, and R.sub.5 form a six-membered aromatic
ring.
[0033] In one embodiment, the azole of structure (IV) is not
substituted. Exemplary unsubstituted azoles applicable for use in
the composition of the present invention are shown in Table I.
Preferred unsubstituted azoles include imidazole, triazole,
pyrazole, benzimidazole, purine, imidazo[4,5-b]pyridine, and
benzotriazole. Among these, benzimidazole is particularly
preferred.
TABLE-US-00001 TABLE I Azoles Name Structure Pyrrole (1H-azole)
##STR00003## Imidazole (1,3-diazole) ##STR00004## Pyrazole
(1,2-diazole) ##STR00005## 1,2,3-triazole ##STR00006##
1,2,4-triazole ##STR00007## Tetrazole ##STR00008## Isoindole
##STR00009## Indole (1H- Benzo[b]pyrrole) ##STR00010##
Benzimidazole (1,3-benzodiazole) ##STR00011## Indazole (1,2-
benzodiazole ##STR00012## 1H-Benzotriazole ##STR00013##
2H-Benzotriazole ##STR00014## Imidazo[4,5-b] pyridine ##STR00015##
Purine (7H-Imidazo (4,5-d)pyrimidine) ##STR00016## Pyrazolo[3,4-d]
pyrimidine ##STR00017## Triazolo[4,5-d] pyrimidine ##STR00018##
[0034] In one embodiment, the azole of structure (IV) is a
substituted azole. In one embodiment, the azole compound is a
substituted imidazole, which has the following general structure
(V):
##STR00019##
wherein R.sub.22, R.sub.44, and R.sub.55 are as defined in
connection with structure (IV).
[0035] In one embodiment, the azole compound is a 2-substituted
imidazole, which has the following general structure (VI):
##STR00020##
wherein R.sub.22 is as defined in connection with structure
(IV).
[0036] In one embodiment, the azole compound is a 2,4-substituted
imidazole, which has the following general structure (VII):
##STR00021##
Wherein R.sub.55 may be hydrogen or methyl, and the various R
groups may be hydrogen, alkyl, halide, alkoxy, alkylamino, cyano,
and nitro. Preferably, the A groups are hydrogen or halide. The
halide may be chloride, bromide, or iodide, and preferably, the
halide is chloride.
[0037] In one embodiment, the azole compound is a benzimidazole
derivative, which has the following general structure (VIII):
##STR00022##
wherein
[0038] R.sub.22 is as defined in connection with structure (IV);
and
[0039] R.sub.66, R.sub.77, R.sub.88, and R.sub.99 are independently
selected from among hydrogen, halide, nitro, and substituted or
unsubstituted hydrocarbyl, substituted or unsubstituted alkoxy,
substituted or unsubstituted amino, and cyano.
[0040] In the context of structure (VIII), the halide may be
selected from among chloride, bromide, and iodide. Preferably, the
halide is chloride.
[0041] Moreover, the substituted or unsubstituted hydrocarbyl may
be selected from among substituted or unsubstituted alkyl,
substituted or unsubstituted alkenyl, substituted or unsubstituted
alkynyl, and substituted or unsubstituted aryl. The substituted or
unsubstituted hydrocarbyl typically has from one to about twenty
five carbon atoms, more typically from one to about twelve carbon
atoms, such as one to about seven carbon atoms. The hydrocarbyl may
be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,
tert-butyl, a pentyl, a hexyl, a heptyl, phenyl, or benzyl. Typical
substituents on substituted hydrocarbyl include nitro, amino,
halide, cyano, carbonyl, carboxyl, hydroxyl, and alkoxy. A
preferred substituent is halide, which may be chloride, bromide, or
iodide. Preferably, the halide substituent is chloride.
[0042] Additionally, the substituted or unsubstituted alkoxy and
substituted or unsubstituted amino typically have from one to about
twenty five carbon atoms, more typically from one to about twelve
carbon atoms, such as one to about six carbon atoms. Typical
substituents on substituted alkoxy and substituted amine include
nitro, amino, halide, cyano, carbonyl, carboxyl, hydroxyl, and
alkoxy.
[0043] In one embodiment, the azole component is a 2-substituted
benzimidazole, which has the following general structure (IX):
##STR00023##
wherein R.sub.22 is as defined in connection with structure
(IV).
[0044] Exemplary substituted azoles include
2-(3,4-dichlorobenzyl)-benzimidazole; 2-bromobenzyl benzimidazole;
2-bromophenyl benzimidazole; 2-bromoethylphenyl benzimidazole;
2-chlorobenzyl benzimidazole; 2-chlorophenyl benzimidazole; and
2-chloroethylphenyl benzimidazole.
[0045] The molecule that comprises at least one organic functional
group that interacts with and protects copper surfaces may be
present in the composition at a concentration of at least about 0.1
g/L. The concentration is typically at or above this minimum
concentration to achieve adequate coverage of the substrate for
corrosion protection. Typically, the concentration of the molecule
that comprises at least one organic functional group that interacts
with and protects copper surfaces is at least about 1.0 g/L, more
typically at least about 4.0 g/L. The molecule that comprises at
least one organic functional group that interacts with and protects
copper surfaces may be present in the composition at a
concentration up to the solubility limit. Typically, the
concentration of the molecule that comprises at least one organic
functional group that interacts with and protects copper surfaces
is at most about 10.0 g/L. Accordingly, the concentration of the
molecule that comprises at least one organic functional group that
interacts with and protects copper surfaces may be between about
0.1 g/L up to the solubility limit in the composition, typically
between about 1.0 g/L and about 10 g/L, more typically between
about 4.0 g/L and about 10 g/L.
[0046] The composition is preferably an aqueous solution comprising
the organic molecules as described above. The composition of the
present invention may further comprise an alcohol, a surfactant,
and an alkaline pH adjuster.
[0047] Incorporating an alcohol in the composition enhances the
solubility of the organic molecules. Applicable alcohols include
alcohols, diols, triols, and higher polyols. Suitable alcohols
include ethanol, propanol, isopropanol, n-butanol, isobutanol,
tert-butanol, ethylene glycol, propane-1,2-diol, butane-1,2-diol,
butane-1,3-diol, butane-1,4-diol, propane-1,3-diol, hexane-1,4-diol
hexane-1,5-diol, hexane-1,6-diol, 2-methoxyethanol,
2-ethoxyethanol, 2-propoxyethanol, 2-butoxyethanol, etc. Then there
are unsaturated diols, such as butene-diol, hexene-diol, and
acetylenics such as butyne diol. A suitable triol is glycerol.
Additional alcohols include triethylene glycol, diethylene glycol,
diethylene glycol methyl ether, triethylene glycol monomethyl
ether, triethylene glycol dimethyl ether, propylene glycol,
dipropylene glycol, allyl alcohol, furfuryl alcohol, and
tetrahydrofurfuryl alcohol.
[0048] The alcohol may be present in the composition at a
concentration of at least about 10 mL/L. Typically, the
concentration of the alcohol is at least about 100 mL/L, more
typically at least about 150 mL/L. The alcohol may be present in
the composition at a concentration up to its solubility limit in
water. It is within the scope of the invention to employ solvent
systems comprised entirely of alcohol. In aqueous solvent systems
wherein the alcohol is a supplementary solvent, the concentration
of the alcohol is typically less than about 500 mL/L, more
typically less than about 200 mL/L. Accordingly, the alcohol
concentration may be between about 10 mL/L and about 500 mL/L,
typically between about 150 mL/L and about 200 mL/L.
[0049] A surfactant may be added to enhance the wettability of the
copper and silver surfaces. The surfactant may be cationic,
anionic, non-ionic, or zwitterionic. A particular surfactant may be
used alone or in combination with other surfactants. One class of
surfactants comprises a hydrophilic head group and a hydrophobic
tail. Hydrophilic head groups associated with anionic surfactants
include carboxylate, sulfonate, sulfate, phosphate, and
phosphonate. Hydrophilic head groups associated with cationic
surfactants include quaternary amine, sulfonium, and phosphonium.
Quaternary amines include quaternary ammonium, pyridinium,
bipyridinium, and imidazolium. Hydrophilic head groups associated
with non-ionic surfactants include alcohol and amide. Hydrophilic
head groups associated with zwitterionic surfactants include
betaine. The hydrophobic tail typically comprises a hydrocarbon
chain. The hydrocarbon chain typically comprises between about six
and about 24 carbon atoms, more typically between about eight to
about 16 carbon atoms.
[0050] Exemplary anionic surfactants include alkyl phosphonates,
alkyl ether phosphates, alkyl sulfates, alkyl ether sulfates, alkyl
sulfonates, alkyl ether sulfonates, carboxylic acid ethers,
carboxylic acid esters, alkyl aryl sulfonates, and sulfosuccinates.
Anionic surfactants include any sulfate ester, such as those sold
under the trade name ULTRAFAX, including, sodium lauryl sulfate,
sodium laureth sulfate (2 EO), sodium laureth, sodium laureth
sulfate (3 EO), ammonium lauryl sulfate, ammonium laureth sulfate,
TEA-lauryl sulfate, TEA-laureth sulfate, MEA-lauryl sulfate,
MEA-laureth sulfate, potassium lauryl sulfate, potassium laureth
sulfate, sodium decyl sulfate, sodium octyl/decyl sulfate, sodium
2-ethylhexyl sulfate, sodium octyl sulfate, sodium nonoxynol-4
sulfate, sodium nonoxynol-6 sulfate, sodium cumene sulfate, and
ammonium nonoxynol-6 sulfate; sulfonate esters such as sodium
.alpha.-olefin sulfonate, ammonium xylene sulfonate, sodium xylene
sulfonate, sodium toluene sulfonate, dodecyl benzene sulfonate, and
lignosulfonates; sulfosuccinate surfactants such as disodium lauryl
sulfosuccinate, disodium laureth sulfosuccinate; and others
including sodium cocoyl isethionate, lauryl phosphate, any of the
ULTRAPHOS series of phosphate esters, Cyastat.RTM. 609
(N,N-Bis(2-hydroxyethyl)-N-(3'-Dodecyloxy-2'-Hydroxypropyl)Methyl
Ammonium Methosulfate) and Cyastat.RTM. LS
((3-Lauramidopropyl)trimethylammonium methylsulfate), available
from Cytec Industries.
[0051] Exemplary cationic surfactants include quaternary ammonium
salts such as dodecyl trimethyl ammonium chloride, cetyl trimethyl
ammonium salts of bromide and chloride, hexadecyl trimethyl
ammonium salts of bromide and chloride, alkyl dimethyl benzyl
ammonium salts of chloride and bromide, and the like. In this
regard, surfactants such as Lodyne 106A (Fluoroalkyl Ammonium
Chloride Cationic Surfactant 28-30%) and Ammonyx 4002 (Octadecyl
dimethyl benzyl ammonium chloride Cationic Surfactant) are
particularly preferred.
[0052] In a preferred embodiment, the surfactant is non-ionic. A
class of non-ionic surfactants includes those comprising polyether
groups, based on, for example, ethylene oxide (EO) repeat units
and/or propylene oxide (PO) repeat units. These surfactants are
typically non-ionic. Surfactants having a polyether chain may
comprise between about 1 and about 36 EO repeat units, between
about 1 and about 36 PO repeat units, or a combination of between
about 1 and about 36 EO repeat units and PO repeat units. More
typically, the polyether chain comprises between about 2 and about
24 EO repeat units, between about 2 and about 24 PO repeat units,
or a combination of between about 2 and about 24 EO repeat units
and PO repeat units. Even more typically, the polyether chain
comprises between about 6 and about 15 EO repeat units, between
about 6 and about 15 PO repeat units, or a combination of between
about 6 and about 15 EO repeat units and PO repeat units. These
surfactants may comprise blocks of EO repeat units and PO repeat
units, for example, a block of EO repeat units encompassed by two
blocks of PO repeat units or a block of PO repeat units encompassed
by two blocks of EO repeat units. Another class of polyether
surfactants comprises alternating PO and EO repeat units. Within
these classes of surfactants are the polyethylene glycols,
polypropylene glycols, and the polypropylene glycol/polyethylene
glycols.
[0053] Yet another class of non-ionic surfactants comprises EO, PO,
or EO/PO repeat units built upon an alcohol or phenol base group,
such as glycerol ethers, butanol ethers, pentanol ethers, hexanol
ethers, heptanol ethers, octanol ethers, nonanol ethers, decanol
ethers, dodecanol ethers, tetradecanol ethers, phenol ethers, alkyl
substituted phenol ethers, .alpha.-naphthol ethers, and
.beta.-naphthol ethers. With regard to the alkyl substituted phenol
ethers, the phenol group is substituted with a hydrocarbon chain
having between about 1 and about 10 carbon atoms, such as about 8
(octylphenol) or about 9 carbon atoms (nonylphenol). The polyether
chain may comprise between about 1 and about 24 EO repeat units,
between about 1 and about 24 PO repeat units, or a combination of
between about 1 and about 24 EO and PO repeat units. More
typically, the polyether chain comprises between about 8 and about
16 EO repeat units, between about 8 and about 16 PO repeat units,
or a combination of between about 8 and about 16 EO and PO repeat
units. Even more typically, the polyether chain comprises about 9,
about 10, about 11, or about 12 EO repeat units; about 9, about 10,
about 11, or about 12 PO repeat units; or a combination of about 9,
about 10, about 11, or about 12 EO repeat units and PO repeat
units.
[0054] An exemplary .beta.-naphthol derivative non-ionic surfactant
is Lugalvan BNO12 which is a .beta.-naphtholethoxylate having 12
ethylene oxide monomer units bonded to the naphthol hydroxyl group.
A similar surfactant is Polymax NPA-15, which is a polyethoxylated
nonylphenol. Another surfactant is Triton.RTM.-X100 nonionic
surfactant, which is an octylphenol ethoxylate, typically having
around 9 or 10 EO repeat units. Additional commercially available
non-ionic surfactants include the Pluronic.RTM. series of
surfactants, available from BASF. Pluronic.RTM. surfactants include
the P series of EO/PO block copolymers, including P65, P84, P85,
P103, P104, P105, and P123, available from BASF; the F series of
EO/PO block copolymers, including F108, F127, F38, F68, F77, F87,
F88, F98, available from BASF; and the L series of EO/PO block
copolymers, including L10, L101, L121, L31, L35, L44, L61, L62,
L64, L81, and L92, available from BASF.
[0055] Additional commercially available non-ionic surfactants
include water soluble, ethoxylated nonionic fluorosurfactants
available from DuPont and sold under the trade name Zonyl.RTM.,
including Zonyl.RTM. FSN (Telomar B Monoether with Polyethylene
Glycol nonionic surfactant), Zonyl.RTM. FSN-100, Zonyl.RTM. FS-300,
Zonyl.RTM. FS-500, Zonyl.RTM. FS-510, Zonyl.RTM. FS-610, Zonyl.RTM.
FSP, and Zonyl.RTM. UR. Other non-ionic surfactants include the
amine condensates, such as cocoamide DEA and cocoamide MEA, sold
under the trade name ULTRAFAX. Other classes of nonionic
surfactants include acid ethoxylated fatty acids
(polyethoxy-esters) comprising a fatty acid esterified with a
polyether group typically comprising between about 1 and about 36
EO repeat units. Glycerol esters comprise one, two, or three fatty
acid groups on a glycerol base.
[0056] The surfactant may be present in the preferred composition
at a concentration of at least about 0.01 g/L. Many surfactants
provide effective wetting at very low concentrations. The minimum
concentration may be adjusted to achieve adequate wetting, which
depends in part on the identity of the surfactant. Typically, the
surfactant concentration is at least about 0.1 g/L, more typically
at least about 0.5 g/L. The surfactant may be present in the
anti-corrosion composition at a concentration of less than about
10.0 g/L. Typically, the surfactant concentration is less than
about 5.0 g/L, more typically less than about 2.0 g/L.
[0057] The composition of the present invention preferably has a pH
between about 1.0 and about 12.0, typically between about 7.0 and
about 11.0. The composition is preferably alkaline because in
alkaline solution, the formation of the protective organic coating
is more rapid than its formation in acidic solution. Alkaline
adjustment may be accomplished using alkaline pH adjusting agents,
such as sodium hydroxide, potassium hydroxide, hydroxides of
quaternary amines, such as tetramethylammonium hydroxide,
tetraethylammonium hydroxide, and the like. Typically, the
concentration of the alkaline pH adjuster is sufficient to achieve
the desired alkaline pH and may be between about 0.01 g/L and about
10.0 g/L, typically between about 0.01 g/L and about 2.0 g/L, more
typically between about 0.1 g/L and about 0.5 g/L.
[0058] In one particularly preferred embodiment, the composition
contains no alkali metal hydroxide, and only an alternative agent
such as sodium tetra borate is used for pH adjustment.
[0059] Another aspect of the present invention is directed to a
method of enhancing the corrosion resistance of a solderable copper
substrate having a precious metal coating on a surface thereof. The
method involves exposing the copper substrate having the precious
metal coating on a surface thereof to a composition comprising a
molecule comprising at least one organic functional group interacts
with and protects copper surfaces and a molecule comprising at
least one organic functional group interacts with and protects
precious metal surfaces.
[0060] In one embodiment, the precious metal coating comprises
silver. The silver coating layer may be deposited on the copper
substrate by an immersion-plated silver coating method known in the
art. For example, the method of coating a copper substrate with
immersion-plated silver described in U.S. Pub. No. 2006/0024430,
herein incorporated by reference in its entirety, is applicable.
Commercially available chemistries for immersion silver coating
include AlphaSTAR.RTM., available from Enthone Inc. (West Haven,
Conn.).
[0061] In one embodiment, the precious metal coating comprises
gold. The gold coating layer may be deposited on the copper
substrate by an immersion-plated gold coating method known in the
art. Typically, the immersion-plated gold coating is deposited over
a base metal underlayer, that is deposited directly on the copper
substrate. Typical base metal underlayers include nickel layers and
cobalt layers, each of which may be deposited by electroless
deposition. For example, a commercially available chemistry for
depositing an immersion gold coating on electroless nickel
underlayer is SEL-REX.RTM. Select, available from Enthone Inc.
(West Haven, Conn.).
[0062] The composition may be applied to the substrate in any
manner sufficient to achieve adequate coverage of the substrate
surface. By adequate, it is meant that the method of exposure
ensures that areas of bare copper are covered with the composition,
for example, copper-silver interfaces at high aspect ratio blind
vias and plated through holes in PCB substrates having immersion
silver finishes and pores that may be present in the immersion
silver coating. Adequate coverage ensures that the molecules in the
composition can interact with bare copper surfaces and precious
metal surfaces in a manner sufficient to form protective organic
film over the copper and precious metal surfaces. Exposure may be
by flooding, dip, cascade, or spraying. Typical exposure times may
be at least about 10 seconds, such as between about 30 seconds and
about 120 seconds, or between about 30 seconds and about 60
seconds. Accordingly, the method of the present invention achieves
rapid substrate coating. The temperature of the composition may
vary between room temperature up to about 55.degree. C., such as
between about 20.degree. C. and about 45.degree. C. or between
about 25.degree. C. and about 45.degree. C. To enhance exposure of
bare copper areas to the coating, exposure may be accompanied by,
for example, scrubbing, brushing, squeegeeing, agitation, stirring,
etc. After exposing the copper substrate to the composition, the
substrate may be rinsed, typically with deionized water for between
about 10 seconds to about 2 minutes.
[0063] Another aspect of the present invention is directed to a
protective organic film applied over an immersion-plated silver
coating deposited on a solderable copper substrate. Exposure of the
copper substrate having an immersion-plated silver coating thereon
to the composition of the present invention results in a protective
organic film on both the silver surfaces and exposed copper
surfaces. The protective organic film comprises both the molecule
comprising at least one organic functional group which interacts
with and protects copper surfaces and the molecule comprising at
least one organic functional group which interacts with and
protects silver surfaces. A depiction of this protective organic
film is shown in FIG. 1, in which the functional groups of the
molecules that constitute the protective organic film are shown
interacting with both the copper substrate and the immersion silver
coating, e.g., the azole interacts with and protects the copper
surface and the mercaptan group interacts with and protects the
silver layer.
[0064] The molecules interact with and form a protective organic
film over the copper and precious metal surfaces by self-assembled
adsorption. Accordingly, the molecules self-assemble into a
monolayer on the copper and silver surfaces. Accordingly, the
protective organic film is a relatively dense, hydrophobic film
that can provide enhanced protection against atmospheric moisture,
which in turn, enhances the immersion silver coating's resistance
to corrosion and sulfidation.
[0065] The protective organic film of the present invention may be
additionally characterized by high thermal stability, particularly
to temperatures commonly reached during lead-free reflow. The
protective organic coatings of the present invention can better
withstand reflow temperatures compared to conventional organic
coatings (such as OSP) as shown by differential scanning
calorimetry and thermogravimetric analysis. For example, a
protective organic coating is stable at temperatures as high as
about 254.degree. C., while only 5% of the film is lost at
temperatures as high as 274.degree. C. This compares favorably to
typical reflow temperatures for tin-lead eutectic solder which is
typically reflowed at temperatures between about 230.degree. C. and
about 240.degree. C. Moreover, the protective organic coating can
withstand multiple lead-free reflow processes.
[0066] Finally, the protective organic coating has been observed to
not negatively impact visual appearance and the solderability of
the copper substrate. Solderability is shown by wetting balance
testing and contact resistance.
[0067] Having described the invention in detail, it will be
apparent that modifications and variations are possible without
departing from the scope of the invention defined in the appended
claims.
Example 1
Immersion Silver Plating Over a Copper Substrate
[0068] A copper cladded FR-4 laminate substrate was plated with a
layer of immersion silver using AlphaSTAR.RTM. chemistry (available
from Enthone Inc., West Haven, Conn.). The copper cladded FR-4
laminate substrate was dipped in an immersion silver plating bath
comprising: [0069] Silver ions (3.0 g/L) [0070] AlphaSTAR.RTM.
additives (300 mL/L) [0071] Balance water.
[0072] The copper cladded FR-4 laminate substrate was dipped in the
immersion silver plating bath for three minutes to deposit thin
silver layers over the copper cladding, the silver layers having an
approximate thickness of about 0.2 .mu.m. A photograph of the
freshly silver-plated laminate substrate is shown in FIG. 2A. The
photograph shows a lustrous silver coating.
Example 2
Hydrogen Sulfide Porosity Testing of Immersion-Plated Silver
Coating on a Copper Substrate
[0073] The freshly silver-plated copper cladded FR-4 laminate
substrate of Example 1 was subjected to a porosity test in a
sulfidizing atmosphere for ten minutes. In this test, the substrate
is exposed to two ambient atmospheres, each comprising a
sulfur-containing gas. In a first glass desiccator (150 mm inner
diameter), an SO.sub.2 vapor is evolved by placing a beaker
containing 150 mL of a 6% solution of sulfurous acid therein and
sealing the desiccator. In a second glass desiccator (150 mm inner
diameter), an H.sub.2S vapor is evolved by placing a beaker
containing 1 mL of a 23.5% solution of (NH.sub.4).sub.2S in 100 mL
distilled water therein and sealing the desiccator. The test is
carried out by placing the laminate substrate in the desiccator
comprising SO.sub.2 vapor first for 24 hours and then placing the
laminate substrate in the desiccator comprising H.sub.2S vapor.
[0074] Photographs of the laminate substrate were taken after two
minutes (FIG. 2B) of H.sub.2S exposure, after five minutes (FIG.
2C) of H.sub.2S exposure, and after ten minutes (FIG. 2D) of
H.sub.2S exposure. The copper in the laminate substrate became
increasingly discolored due to the formation of silver sulfides
(AgS.sub.x), copper oxides (CuO.sub.x), and copper sulfides
(CuS.sub.x). It is apparent, therefore, that a self-limiting
immersion-plated silver coating may not be sufficient to protect
copper from corrosion.
Example 3
Applying a Protective Organic Coating Comprising a Mercaptan
Compound to an Immersion-Plated Silver Coating on a Copper
Substrate
[0075] Three copper cladded FR-4 laminate substrates were plated
using the AlphaSTAR.RTM. chemistry according to the method shown in
Example 1. The copper cladded FR-4 laminate substrates were dipped
in a commercially available post-treating composition comprising a
mercaptan compound. The post-treating composition was Evabrite
WS.RTM. (available from Enthone Inc., West Haven, Conn.) The
post-treating composition comprised the following components:
[0076] 1% wt./vol. Evabrite WS.RTM. additives [0077] Balance
water.
[0078] The laminate substrates were dipped according to the
parameters shown in Table II. After dipping, the relative atomic %
of each of the elements silver, carbon, oxygen, and sulfur on the
surface of the silver-plated laminate substrates coated with
Evabrite WS.RTM. were determined by X-ray photoelectron
spectroscopy. The results are shown in Table III.
TABLE-US-00002 TABLE II Dipping Parameters Laminate Substrate
Number Temperature Duration 1 25.degree. C. 30 seconds 2 25.degree.
C. 5 minutes 3 50.degree. C. 30 seconds
TABLE-US-00003 TABLE III Atomic % of Ag, C, O, and S on the Surface
Of the Silver-Coated Laminate Substrates Relative Laminate
Substrate Atomic % of Element Number Ag C O S As Plated 52.9 34.1
13 0 1 37.6 54.3 6.5 1.5 2 30.9 60.7 6.9 1.5 3 23.4 72.6 1.5
2.6
[0079] Surface coverage, according to the relative atomic % of
sulfur and carbon, of mercaptan was not substantially increased by
increasing dipping time from 30 seconds to 5 minutes. Moreover,
dipping for five minutes did not lead to an appreciable reduction
in surface oxygen compared to dipping for 30 seconds. Accordingly,
an effective mercaptan coating can be applied in as little as 30
seconds.
[0080] Surface coverage increased by at least 50%, as measured by
relative atomic % of sulfur, when the silver-plated laminate
substrate was dipped in the Evabrite WS.RTM. composition at
50.degree. C. Moreover, the surface oxygen atomic % was
substantially reduced when the laminate substrate was dipped in the
composition at 50.degree. C. Without being bound to a particular
theory, it is thought that the higher temperature catalyzed the
formation of the mercaptan self-assembled monolayer over the silver
coating. That is, the higher temperature catalyzed the formation of
chemical bonds between silver atoms and sulfur and catalyzed bond
breaking between silver atoms and oxygen. Moreover, it is thought
that the higher temperatures reduces the composition's surface
tension, which effects better wetting and thus better penetration
by the mercaptan molecules into silver pores. With better pore
penetration, it may be concluded that the mercaptan more
effectively blocks the migration of copper atoms through the silver
pores and inhibits copper oxidation.
Example 4
Hydrogen Sulfide Porosity Testing of Non-Coated Silver-Plated
Laminate Substrate and Mercaptan-Coated Silver-Plated Laminate
Substrate
[0081] To determine the effectiveness of using Evabrite WS.RTM.
compositions for protecting silver-plated laminate substrate
against corrosion, Laminate Substrate 1 from Example 3 and a
freshly silver-plated Laminate Substrate plated according to the
method of Example 1 with no post-treatment were subjected to a
H.sub.2S porosity test for ten minutes, as described above in
Example 2. A photograph of the untreated silver-plated laminate
substrate is shown in FIG. 3A, and the Evabrite WS.RTM.-treated
silver-plated laminate substrate is shown in FIG. 3B. The Evabrite
WS.RTM.-treated silver-plated laminate substrate retained its
lustrous silver color while the untreated silver-plated laminate
substrate became tarnished and discolored.
Example 5
Post-Treatment Composition Comprising a Compound Comprising a
Mercaptan Functional Group
[0082] A post-treating composition was prepared having the
following components: [0083] 0.08% wt./vol. 1-octadecanethiol
[0084] Balance water.
Example 6
Post-Treating Composition Comprising a Compound Comprising an
Aromatic Heterocycle Comprising Nitrogen
[0085] A post-treating composition was prepared having the
following components: [0086] 0.09% wt./vol.
2-(3,4-dichlorobenzyl)-benzimidazole [0087] Balance water.
Example 7
Post-Treating Composition Comprising a Compound Comprising an
Aromatic Heterocycle Comprising Nitrogen and a Compound Comprising
a Mercaptan Functional Group
[0088] A post-treating composition was prepared having the
following components: [0089] 1% wt./vol. Evabrite WS.RTM. additives
[0090] 0.09% wt./vol. 2-(3,4-dichlorobenzyl)-benzimidazole [0091]
Balance water.
Example 8
Hydrogen Sulfide Porosity Testing of Untreated and Post-Treated
Silver-Plated Copper Coupons
[0092] Several immersion silver plated copper cladded FR-4 laminate
substrates were subjected to an H.sub.2S porosity test (45 minutes
exposure to H.sub.2S vapor), as described above in Example 2. The
immersion silver plated copper cladded FR-4 laminate substrates
were either left untreated or post-treated with the compositions
described in Examples 3, 5, 6, and 7. Table IV shows the coupons
identified by the post-treatment composition according to Example
Number and the appearance of the coupons after the 45 minute
H.sub.2S porosity test. Photographs (FIG. 4A to 4F) were taken of
each coupon after the 45 minute H.sub.2S porosity test.
TABLE-US-00004 TABLE IV Post-Treatment Number Composition
Appearance FIG. 4 4 Untreated Dark Blue A 5 Example 6 Brown/Blue B
6 Example 3, coupon 1 Brown C 7 Example 5 Slightly Brown D 8
Example 7 No tarnishing E 9 Example 3, coupon 3 No tarnishing F
[0093] Coupons 8 and 9, depicted in FIGS. 4E and 4F, showed little
or no tarnishing even after 45 minutes of exposure to H.sub.2S.
Accordingly, post-treating methods involving applying a mercaptan
at elevated temperatures or applying a mercaptan and an aromatic
heterocycle comprising nitrogen are effective means for inhibiting
tarnishing even under highly corrosive environmental
conditions.
Example 9
Bake Testing After Hydrogen Sulfide Porosity Testing of Untreated
and Post-Treated Silver-Plated Copper Coupons
[0094] Six immersion silver plated copper cladded FR-4 laminate
substrates were either untreated or post-treated in the same manner
as coupons 4-9 in Example 8. The six immersion silver plated copper
cladded FR-4 laminate substrates were subjected to an H.sub.2S
porosity test (45 minutes exposure to H.sub.2S vapor) followed by
baking at 5 minutes at 250 to 257.degree. C. Photographs (FIG. 5A
to 5E) were taken of each laminate substrate after this treatment.
The laminate substrate depicted in FIG. 5D, which was treated with
mercaptan and an aromatic heterocycle comprising nitrogen exhibited
the least tarnishing/corrosion compared to the other
post-treatments.
[0095] In view of the above, it will be seen that the several
objects of the invention are achieved and other advantageous
results attained.
[0096] When introducing elements of the present invention or the
preferred embodiment(s) thereof, the articles "a", "an", "the" and
"said" are intended to mean that there are one or more of the
elements. For example, that the foregoing description and following
claims refer to "a" layer means that there can be one or more such
layers. The terms "comprising", "including" and "having" are
intended to be inclusive and mean that there may be additional
elements other than the listed elements.
[0097] As various changes could be made in the above without
departing from the scope of the invention, it is intended that all
matter contained in the above description and shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
* * * * *